1. Field of the Invention
The present invention generally relates to a circuit breaker. More specifically, the invention is directed to an arc extinguishing, or shooting apparatus for contacts of a multi-pole circuit interrupting apparatus (circuit breaker).
2. Description of the Related Art
In general, circuit breakers including arc extinguishing apparatuses for contacts have been widely used to electrically interrupt power source lines when overcurrent flows through the power source lines. One of these conventional circuit breakers having arc extinguishing, or shooting apparatuses is described in, for instance, Japanese KOKAI (Disclosure) Utility Model Application No. 52-71051 opened on May 27, 1977 filed by Mitsubishi DENKI K.K.
Referring now to FIGS. 1 and 2, this conventional circuit breaker having the conventional arc extinguishing apparatus will be described.
FIG. 1 is a fragmentary sectional side view of one pole (single phase) of the conventional circuit breaker including the conventional arc extinguishing apparatus and FIG. 2 is a plan view of the arc extinguishing apparatus of FIG. 1. Referring to FIG. 2, reference numeral 1 denotes a case for the circuit breaker, 101 denotes its side wall, 2 denotes a movable contact member coupled with a movable contact controller (not shown), 201 denotes its movable contact, 3 denotes a fixed contact member, and 301 denotes its fixed contact. Reference numeral 4 denotes the conventional arc extinguishing apparatus for extinguishing an arc formed between the contacts 201 and 301 at the time when the circuit current flowing through these contacts 201 and 301 is interrupted, 5 denotes an external conductor, 6 denotes an external connection terminal for connecting the external conductor 5 to the fixed contact member 3, 601 denotes a screw for attaching the external connection terminal 6 to the fixed contact member 3, and 602 denotes a screw for securely clamping the external conductor 5 to the external connection terminal 6. Reference numeral 7 denotes an insulating partition disposed between the arc extinguishing apparatus 4 and the external connection terminal 6, and 8 denotes an arc runner disposed on the fixed contact member 3.
The conventional arc extinguishing apparatus 4 is constructed of a plurality of substantially U-formed arc extinguishing plates 401 opening on the side of the movable and fixed contact members 2, 3 held by side support plates 402 in a stacked condition in the vertical direction (viewed in FIG. 1) spaced apart from one another, and having two leg portions 403 of each arc extinguishing plate 401. Reference numeral 9 denotes an insulating plate made of inorganic material such as mica and asbestos which is disposed on both inside surfaces of the two leg portions 403.
Operation will be briefly described below. When a higher current such as an overcurrent flows through the movable and fixed contacts 201, 301 also closed, the movable contact member 2 is separated from the fixed contact member 3 by means of the movable contact controller, whereby the contacts 201, 301 are opened and an arc is formed between these contacts 201, 301. At that time, the arc is driven and expanded in the direction of the inner portion 405, or base, of the arc extinguishing plate 401, i.e., toward the right in FIG. 2, by electromagnetic action between the magnetic flux produced through the arc extinguishing plate 401 due to the arc current (the magnetic flux produced by eddy current) and the arc current itself, so that the arc is divided into sections and cooled down by the arc extinguishing plates 401 so as to be extinguished. The function of the insulating plate 9, in such an arc extinguishing process, is to prevent the arc extinguishing plate 401 from being melted under the heat of the arc and from being, further, scattered. Besides, as suggested in the above-mentioned Japanese KOKAI (Disclosure) Utility Model Application No. 52-71051 (1977). the insulating plate 9 serves the function to prevent the arc from jumping from the end or side of the movable contact 201 or the movable contact member 2 to the leg portions 403 of the arc extinguishing plate 401 and stagnating there to make the interruption of the current unachievable.
However, since the insulating plate 9 is formed of an inorganic material, the surface of the insulating plate 9 goes into a melted condition under the higher heat of the arc during the circuit breaking operation. As a result, while the arc current is at the zero-cross point, the insulation recovery capability between the movable and fixed contacts will be deteriorated thereby making the current interruption impossible. There are also such problems with the prior art insulating plates that they are not mass-producible, higher in manufacturing cost, brittle due to their high hardness, easily broken by vibrational shocks, and further, easily affected by heat shocks, for example, cracks are formed on the surface of the insulating plate 9 while serving subjected to the arc.
The present invention has been made in view of these conventional drawbacks, and therefore, an object of the present invention is to provide an arc extinguishing apparatus including insulating plates not causing inability of current interruption, mass-producible at low cost, hardly broken by vibrational shocks, and further, resistive to heat shocks from the arc.
Another object of the present invention is to provide a circuit interrupting apparatus including an arc extinguishing apparatus having various advantages as described above.